Background. Almost all nursing homes in the United States are required by the 1987 Omnibus Budget Reconciliation Act to assess each resident's functional, medical, psychosocial, and cognitive status using a standard instrument known as the Minimum Data Set (MDS). We report a validation study to show that the MDS Cognitive Performance Scale (CPS), a cognitive measure generated from 5 MDS items (comatose status, decision making, short-term memory, making self understood, and eating) can be used to detect cognitive impairment as denned by the Mini-Mental State Examination (MMSE). Methods. Two hundred subjects were randomly recruited from 8 nursing home facilities in North Carolina. Two medical students administered the MMSE, while a geriatric research nurse was responsible for collecting MDS cognitive items, which included the 5 items required for generating CPS scores. Cognitive impairment was denned by MMSE scores adjusted for education. Agreement between the CPS and the MMSE in identifying cognitively impaired subjects was then evaluated. Results. The CPS showed substantial agreement with the MMSE in the identification of cognitive impairment; the sensitivity was .94 (95% confidence interval [CI]: .90, .98), the specificity was .94 (95% CI: .87, .96), and the diagnostic accuracy as measured by the area under the receiver operating characteristics (ROC) curve was .96 (95% CI: .88, 1.0). Conclusions. The MDS Cognitive Performance Scale, when performed by a trained research nurse using recommended protocols, provides a valid measure of cognitive status in nursing home residents.